Conventionally, a press key 10 is usually constructed with a scissors-type elastic structure as shown in FIG. 1, which comprises: a keycap 13, a substrate 14 and two supporting arms 11, 12 sandwiched between the keycap 13 and the substrate 14. In FIG. 1, the two supporting arms 11, 12 are pivotally coupled with each other at the middle thereof forming an X-shaped structure. Such conventional scissors-type press key 10 is favored for its longer stroke and lower noise, etc., so that it is vastly adopted by those thin-type keyboards in recent year, especially for keyboards of notebook computers. However, such scissors-type press key 10 still has shortcomings. Namely, as the two supporting arms 11, 12 are pivotally coupled with each other at the middle thereof, the X-shaped structure of the two arms 11, 12 can only provide support to a small portion of the keycap 13. Thus, when it is used for supporting a bar-shaped keycap 13, as that shown in FIG. 1, and such keycap 13 is not pressed by a finger 20 exactly at a portion where it is supported by the X-shaped structure of the two arms 11, 12, the pressing of the finger 20 will cause the keycap 13 to tilt and thus the compress block 131 arranged at the bottom of the keycap 13 will not be able to press exactly on the elastic member 15 mounted on the substrate 14. Consequently, the conducting plate arranged at the bottom of the elastic member 15 will not be able to have an exact contact with the circuit board 16 disposed beneath the substrate 14, that is, the contact between the conducting panel and the circuit board is poor.
For preventing the aforesaid slanting from happening, it is commonly seen in the industry to integrally form an enforcement rib at the bottom of the keycap. Following the trend of lighter, thinner and smaller design, it is preferred to have thinner keycap. However, when a key cap is integrally formed with a poorly designed reinforcement structure or with a thick reinforcement structure, such keycap consequently is going to surfer for having a shrinking pressing surface that no only it is not good looking, but also the yield is poor. Moreover, as such reinforcement structure is disposed beneath the keycap, its disposition is restricted by those other structures formed under the keycap in a manner that it is unable to evenly distribute the pressing force over the entire surface of the keycap; and as the structure of such enforcement rib is comparatively complex, the manufacturing cost is increased.